An Application of the PTV-technique to Sea Water Run-up over a Trench near a Tidal Reach

Experiments on a salt-water flow running up over a trench are carried out on the basis of a flow-visualization technique to consider the local hydraulic characteristics of flows around the trench, which is necessary for maintaining or reproducing the function of trench as a habitat. The flow regime inside and outside the trench significantly depends on the aspect ratio of a opening length to a step height of trench. In case that the opening length of trench is shorter than the reattachment length, large eddy motions induced periodically inside the trench by the vortex shedding from the step. The eddies have direct effects upon momentum exchange through the trench-mouth, and reduce the magnitude of velocity inside the trench.